Transplantation of cells exhibiting glucose-responsive insulin secretion has the potential to cure diabetes. However, this approach is limited by an inadequate supply of pancreatic β-cells, the only cells exhibiting the desired property. The development of expanded populations of human β-cells that can be used for cell transplantation is therefore a major goal of diabetes research (D. R. W. Group, “Conquering diabetes: a strategic plan for the 21st century” NIH Publication No. 99-4398 (National Institutes of Health, 1999)). A number of alternative approaches are being pursued to achieve that goal, including using porcine tissue as a xenograft (Groth et al., J Mol Med 77:153-4 (1999)), expansion of primary human β-cells with growth factors and extracellular matrix (Beattie et al., Diabetes 48:1013-9 (1999)), and generation of immortalized cell lines that exhibit glucose-responsive insulin secretion (Levine, Diabetes/Metabolism Reviews 1: 209-46 (1997)). A need exists, therefore, for methods of identifying and purifying cells that exhibit glucose responsive insulin secretion, and for progenitor and/or stem cells capable of differentiating into glucose-responsive insulin-secreting cells.